The procedure and apparatus for utiliziiig the cttrboxylic acid as a solvent in the presence of air and steam have been described.12
(12) \Fr. \V.Kaeding, R. 0. Lindblom, rind It. U. Temple, U. S. Pat. 2,727,926.
rlcl~,~ulcledyn,e,Lt. I 3111 iiidebted t u Alr. li. D. Barnard, 3 1 ~11, . H. ;\lcyer,11~. It, ireiklc, and 3Ir. A. Ti. ,Jolin\oii for inany helpful suggestioii\ when this i\-ork \vas iiiitiiited P I T T ~RC,, B LC I L I ~
Resonance Interactions i n Naphthalene Derivatives : Dissociation of
Substituted Naphthols and Naphthoic Acids
Received .Jamary do, IAb'l In order to compare resonance interactions in 4-X-1-naphthyl derivatives with those in cwrespondirig benzene coinpounds, the thermodynamic pK values, in water a t 25", of a series of substituted I-naphthols have been nienswcd, together with the value for p-hydroxybenzophenone. An explanation has been offered for diffwoiicm in rcw~nttnceinteraction noted for some electron-withdrawing substituents. The p K values, in n - a k r :it 25", of n iiiiniber of sulistitrited 1-nnphtlioic ncitls hrive also heen dptwminpd and have been comparrtl n-ith t,hosr of tlicb rori~esponrliiiglwrixoir~xrids.
In receiit publications Wepster aiid w-\vorkers* aiid Taft aiid his colleague^^^^ have slio~vii, using different approaches, that the concept of discrete sigma values (u+, u-, and U ) is fn1lac:ious. Taft, ut nl. h a w deriioiistrated t'hat, reactivity data for :1 select groiip of mcta-suhstituted pheiiyl groups :ire corrrlal ed by the Haiiiiiiett8 equat'ion with Inuch greater generality uiid precision thaii data for other subst'ituted pheiiyl groups. They designated tho niean sigma values, for this select group of substituent,.;, as uo values. As t>hereis no direct' conjugative intcmctioii between meta substituent' aiid side-chxiii rmctioii center (and caiisequeritly 110 coiit,ributioii, by :i ~'eso~i;uice efTwt, t o the reltt8ive rnte) such u" r-dues are a iiiwsure of the iiiduchvr cffcct of iiii X~--C6H,--group, rclative to the pheiiyl group. Ii'or para-substituted l)eiizeiic> derivatives, conjugat'ioii between thc substitueiit) a,id sidechain reaction center will o(*curt o an extent which will vary from one reaction series t o another and consequently for thrse substituents, a range of sigma values is required. Taft et al. obtained u" values for para-subst it>utedphriipl groups from the reactivities of heiizyl derivat ivcs. 111 t hrhe conipounds r c , w ~ i ~ i nbetween ~~e t hc riiig :uid rmctioii cmeiitcr is pwvciitctl hy the ilitcqmsed incthylciie group.
\Ye 1iaJ.e previously s:hon-u4-6 that t hc Hanimett reaction coiist'aiit ( p ) for alkaliiie hydrolysis of substituted ethyl 1-naphthoates in 85% ethanol at,
SEPTEMBEIE
1961
RESONAKCE INTERACTIONS I N TU'APHTHALENE DERIVATIVES
the relative reactivity. We have also determined the dissociation constant of p-hydroxybenzopherione and, in addition, the pK values of several substituted 1-naphthoic acids. I t was hoped that the latter would provide a second reaction series which could be used to test the conclusion that the inductive effects of correspondingly substituted 1-naphthyl and phenyl groups are equal.
3 149
= 3.75223; potassium hydrogen tartrate, pwH(0.03 rn) = 3.64524; chloroacetic acid-sodium chloroacetate (standard AnalaR chloroacetic acid solution partially neutralized with standard sodium hydroxide solution), p K ~ x= 2.860.25 For an acid HB in 3 buffer mixture of HX and X, ~ K Hwas B obtained using one of the equations.'*
~ K H= B PbVH - log mB/mHB - log.fB/.fClfHB
(1)
+
~ K H= B ~ K H X log mx/max - log mB/mm log f B f H X / f H B f X
(2)
In the case of the naphthols, with one exception, the spectrophotometric determination of mB/mHe was made a t Amax far the appropriate naphthoxide anion, a t which wave Physical constants of compounds examined were: .Yaphthols. 4-methyl-l-naphthol,8 1n.p. 8.7"; I-naphthol, n1.p. length €HB x a s less bhan 2% of E B . For 3-nitro-1-naphthol the ;tcid peak at 380 nip was used. The optical density of some of !)6.5'; l-t~r~ino-l-naphthol,~ m.p. 130"; 4-rhloro-I-naphthe naphthol solutions varied slightly, depending upon the thol.1" iii.1). 119"; 4-hydrosy-l-naphthaldehyde,11 ni.p. age of the solution. Moreover, certain of the solid naphthols I 83"; 4-hcnzo~l-l-na~~lithol,'2 n1.p. 165'; 4-cyano-1-naphthol, I 3 1n.p. 1i7"; 4-nitro-l-naI)hthol,'" ni.1). 188"; 4-nitroso- discolored quite rapidly on standing. The naphthols were I-naphthol, 111.p.200"; 3-nitr0-l-naphtho1,~5m.p. 169"; p - therefore always purified immediately before use and optical density measurements xere made on freshly prepared soluhydroxyl)enzophenoiie,'6 m.p. 135". .Yaphthoic acids. 1-nnphthoic acid, 1n.p. 180"; 4-bromo-1- tions. The dissociation constants now reported are less precise ( f 0.03) than those reported earlier for substituted naphthoic acid.5 ni.1,. 22 1 ; 4-rhloro-I-naphthoic 0.01), which did not show the instability noted 1n.p. 225" ; 4-fluoro-1-n:tphthoic wid. m.p. 224.5-225' ; phenols (=IC in the naphthol series. The naphthoxide solutions were fluo:&methyl-l-naphthoic acid,6 111.p.173.5; 3-riitro-1-naphthoic rescent but the pK determinations were not affected by this; acid," m.p. 269"; 4-nitro-l-11:tphthoic ncid.17 m.p. 225.5'. Chromatography on ahunina \vas found to he satisfactory for in each c:~sc,the solution of naphthoxide in alkali was shown purifying the sinall amounts of n:lphthols required for t o obey Beer's Law. T h e napht,hoic acids were found to be a much less suitable spectrophotometric iiie:ts~ir(~iiic~iits. The eliitiun of the colorless naphthols couhl usliall>. t )(, i'ollo\\ccl by the fliiorescwicc aysteni for spectrophotometric investigation because of the excited by a mercury lamp. sinall spec-tral change which occurs on converting the acid to Thermodynultlic dissociafioth cotbsilui/!s \yere Ineasuretl 1)v :inion. Thus, in thc least favorable case (4-nitro-1-naphthoic the spectrophotoinetric method :IS dtwribcd previously.'x acid) at the \wve length used, eHn/en = 0.82. For the most For these rather insoluble naphthalene tlt:riviltivcs, 4 (mi. favorable case (1-naphthoic acid) CHB/CB = 4.1. These path-length cells were usually requircxl i n order to obtain values ma!. be contrasted with c E B / e B
